Audiologic findings in unilateral deafness resulting from contralateral pontine infarct KAREN JO DOYLE, MD, PhD, CYNTHIAFOWLER, PhD, and ARNOLD STARR, MD, Irvine and Long Beach, California Focal brain stem infarction has been uncommonly from April 1994 demonstratd a dorsally located infarct associated with unilateral sensorineural hearing loss involving the medial left portion of the upper pons, as well (SNHL). Kumar et al. (1986) 1 found a single case of as ischemic changes of the periventricular deep white brain stem infarction among 200 cases of unilateral matter (Figs. 1 and 2). SNHL. Previous case reports of unilateral SNHL He was referred 3 weeks after the stroke to the Audi- ology Department for evaluation of his right-sided hearing after brain stem infarct have been the result of loss. Audiogram revealed a fiat, severe SNHL in the right lesions of the ipsilateral cochlear nuclei in the dor- ear and a moderate high-frequency SNHL above 2000 Hz solateral medulla. 2,3 Wada and Starr (1983) 4 deter- in the left ear (Fig. 3). Speech discrimination was 0% in mined that an experimentally produced lesion of the the right ear and 92% in the left ear. Acoustic reflexes lateral lemniscus produced a unilateral contralateral were absent in the right ear. ABR was performed with abnormality in the N 3 portion of wave III of the condensation and rarefaction dicks presented 10/second auditory brain stem response (ABR) in guinea pigs. at 95 dB nSL (Fig. 4). In the left ear, all components were We report a case of unilateral SNHL after a con- identified, and their intercomponent times were within tralateral focal pontine infarct verified by magnetic normal limits. In the right ear, wave I was present for resonance imaging (MRI) and ABR testing. condensation clicks at 1.98 msec, and no other waves were identified. Transient and distortion-product otoacoustic CASE REPORT emissions (OAEs) were performed. In the right ear, tran- sient emissions were present with energy present through A 63-year-old man with a history of hypertension was 3000 Hz with 81% reproducibility, similar to those ob- admitted to the Veterans Administration Medical Cen- tained from the left ear (Fig. 5). Distortion-product OAEs ter-Long Beach in June 1994 with a urinary tract infec- (2F2 - F1 = 1.221; F1 = 70 dB SPL; F2 = 70 dB SPL) tion. During his admitting physical examination, a neuro- were present across frequencies in the right ear and logic examination was performed that revealed a right- through F2 = 3000 Hz in the left ear. Repeat MRI with sided hearing loss. The neurologic examination was gadolinium of the internal auditory canals was performed, otherwise normal. He reported that he had had a stroke and they were normal. in April 1994 and had spent several days in another hospital. The records and MRI scans from that hospital- DISCUSSION ization were obtained. The admission physical examina- tion from April revealed a blood pressure of 170/86, a Although we used the combined term sensorineu- central right facial palsy, a right-sided hearing loss, nys- ral hearing loss, the majority of patients with SNHL tagmus (direction not given), and unsteady gait. Labora- have lesions of the sensory apparatus, whereas "neu- tory examination revealed normal cerebrospinal fluid ral" lesions, including spiral ganglion degeneration, chemistries and cell counts and negative VDRL. The MRI eighth nerve lesions, and central auditory pathway lesions from the cochlear nuclei to the temporal From the Divisions of Otolaryngology-Head and Neck Sur- cortex, are found less frequentlyJ Among the causes gery and Audiology (Drs. Doyle and Fowler), Veterans of hearing loss, cerebrovascular infarction of the Administration Medical Center; and the Departments of auditory pathways has been described infrequently. Otolaryngology-Head and Neck Surgery (Drs. Doyle and A 1986 report of 200 cases of unilateral SNHL found Fowler) and Neurology (Dr. Starr), University of California Irvine. 42 individuals with confirmed retrocochlear lesions, Received for publication April 28, 1995; revision received June of which there was one lesion adjacent to the co- 27, 1995; accepted July 17, 1995. chlear nucleus and a second patient with a pontine Reprint requests: Karen Jo Doyle, MD, PhD, Department of lesion? The most commonly found central lesions in Otolaryngology-Head and Neck Surgery, University of Cali- that study were cerebellopontine angle tumors, cen- fornia Irvine Medical Center, Bldg. 25, Route 81, 101 The City Dr., Orange, CA 02668. tral nervous system lues, and multiple sclerosis. OTOI.A~YNGOI.HZAO NECK SUnG 1996;114:482-6. Lownie and Parnes (1991) 2 found two cases of ipsi- 23/4/67847 lateral SNHL caused by infarcts of the cerebellum 482 Otolaryngology - Head and Neck Surgery Volume 114 Number 3 DOYLE et al. 483 Fig. I. Coronal T1-weighted MRI of the brain demonstrating left pontine infarct (arrow). Fig. 2. Axial T2-weighted MRI of the brain demonstrating left pontine infarct (arrow). and cochlear nucleus. In both patients there was for the SNHL in 50 patients, 3 of whom had brain significant improvement of the hearing loss in the stem infarcts involving the auditory pathways (one in weeks after infarction. Bales (1989) 3 reported a the cochlear nucleus; the locations of the other two patient with a hearing loss ipsilateral to a pontine were not given). There have been no previous re- infarct who had a moderate-to-severe hearing loss, ports of lesions of the contralateral upper ports poor speech discrimination, and absent waves IV producing hearing loss in human beings. and V, with normal waves I through Ill. The hearing The brain stem auditory pathways are shown in improved l:o normal in 1 month. Armington et al. Fig. 6. The cochlear nerve projects to the dorsal and (1988) 6 performed MRI in 176 patients with SNHL ventral cochlear nuclei in the medulla adjacent to and found an abnormality believed to be responsible the inferior cerebellar peduncle. Second-order neu- Otolaryngology - Head and Neck Surgery 484 DOYLE et al. March .I 996 RIGHT EAR (AD) LEFT EAR (AS) 250 500 1000 2000 4000 8000 250 500 1000 2000 4000 8000 7O ~=1 B/C B0 90 80 9 o l B/C ,5 kHz 1 WHZ 2 kHz 3 kHz 4 kHz 5 WHz 6 kHz .S kHz I Idtz 2 kHz 3 kHz 4 kHz SkHz 6 WHZ PURE-TONE SDT WORD-RECOGNITION MLV AD AS EAR AVERAGE PERFORMANCE ~RECOR~D~ u..*s~oAA~ O X 2 3 7'0 I00 ~, N.I.I. NO.6 ~ FREQ. FREQ. SITr dBHL clBHL dBHL MCL ULL laa~v=/~ n [] /~ MAHYr.AND AD 70 78 0% C.C B/C < > ~:~ i~l~ / ~I~, ~" ~ i~:~ ~ ~:~"ik:~i~ W-22 UNMASKED MASKINGAs ~i~!~:! I: ',:~ ~Li~ SO ~ ~ ~ ~ ~:I P CTURE BI~ ["" '~ ":'~'::~..... , ,,:~, ;;~::;;:;~:~::; IDENTIFICATIONII IlA~¢n I AS 15 15 100% ReL~e..rrY ACOUSTICREFLeXEs MASKING i~ii~ i ~/~:/!~l~i AD ~ ~i,~ ~ ~: :~ ~ i~ i~lii~ ~' ~!~ IPSi A- - -A REMARKS: L,ST, FlnST, MI 0A~ 4/20/94 sso AGe 64 slel VAKICLONG BEACH~ CA VA FORM10"30 (~) REV111R4 Fig. 3. Audiogram of patient demonstrating severe right SNHL and poor speech discrimination. Left ear has normal hearing to 2000 Hz and moderately severe high-frequency SNHL. rons decussate to the contralateral medulla through that the patient in this article, who had bilateral the trapezoid body. Fibers then ascend in the lateral high-frequency cochlear hearing loss, had a right- lemniscus in the pons to the inferior colliculus of the sided neural hearing loss from a brain stem infarc- midbrain. Wada and Start (1983) 4 produced lesions tion in the area of the contralateral pontine lateral of the trapezoid body, lateral lemniscus, or inferior lemniscus. The timing of the hearing loss at the colliculus in guinea pigs to determine the effects on onset of the stroke, and audiogram, ABR, OAE, and the ABR. Lesions of the trapezoid body produced MRI findings all support this theory. The presumed attenuation of ipsilateral waves III, IV, and V. Le- mechanism of the right-sided hearing loss is inter- sions of the inferior colliculus had no effect on the ruption of the auditory pathway at the contralateral ABR. When unilateral lesions of the lateral lemnis- lateral lemniscus. Because the cochlea and cochlear cus were created in 11 animals, ABR to ipsilateral nerve are normal on the right side, OAEs and ABR stimulation was normal, but a loss of the N 3 portion wave I are normal to ipsilateral stimulation in the of wave III evoked by contralateral stimulation was right ear. It is unclear why waves II and III are found, and no changes were noted in waves II or P3. missing to ipsilateral stimulation because they origi- Their previous work in cats had localized P3 to the nate distal to the site of the lesion. Perhaps retro- pons, with components of N 2, P3, and N 3 generated grade neuronal loss occurred. in the brain stem contralateral to the ear stimulated. The patient in this article had normal low-fre- In contrast, Waves I and P2 originate in the ipsilat- quency transient (click) and distortion-product eral cochlear nerve and cochlear nuclei/We posit evoked OAEs. Evoked OAEs are sounds produced Otolaryngol~)y - Head and Neck Surgery Volume ~44 Number 3 DOYLE et al. 485 ABR IPSI CGNTRA __ v ~s J IJJ .J AD =E <[ o :, o 2 4 8 LATENCY(ms) Fig. 4. ABR of patient demonstrating normal responses in the left ear and absent waves il through V in the right ear. The left ear responses have wave V at normal latency to both ipsilateral {IP$1)and contralateral (CONTRA) stimuli (four upper tracings). In the right ear {two lower left tracings), wave I was present for condensation clicks at normal latency, and no waves were identified for contralaterai stimulation (two lower right tracings).